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Magnetic resonance imaging follow-up can
screen for soft tissue changes and evaluate
the short-term prognosis of patients with
developmental dysplasia of the hip after
closed reduction
Xianghong Meng
1
, Jianping Yang
2
and Zhi Wang
1*
Abstract
Background: Magnetic resonance imaging (MRI) can show the architecture of the hip joint clearly and has been
increasingly used in developmental dysplasia of the hip (DDH) confirmation and follow-up. In this study, MRI was
used to observe changes in the hip joints before and after closed reduction (CR) and to explore risk factors of
residual acetabular dysplasia (RAD).
Methods: This is a prospective analysis of unilateral DDH patients with CR and spica cast in our hospital from
October 2012 to July 2018. MRI and pelvic plain radiography were performed before and after CR. The labro-
chondral complex (LCC) of the hip was divided into four types on MRI images. The variation in the thickening rate
of the ligamentum teres, transverse ligaments, and pulvinar during MRI follow-up was analyzed, and the difference
in cartilaginous acetabular head index was evaluated. The “complete relocation”rate of the femoral head was
analyzed when the cast was changed for the last time, and the necrotic rate of the femoral head was evaluated
after 18 months or more after CR. Lastly, the risk factors of RAD were analyzed.
Results: A total of 63 patients with DDH and CR were included. The LCC was everted before CR and inverted after
CR, and the ligamentum teres, transverse ligaments, and pulvinar were hypertrophic before and after CR, and then
gradually returned to normal shape. The cartilaginous acetabular head index gradually increased to normal values.
Complete relocation was observed in 58.7% of femoral heads, while 8.6% had necrosis. The abnormalities in LCC
was related to RAD (OR: 4.35, P= 0.03), and the rate of type 3 LCC in the RAD group was higher. However, the IHDI
classification (P= 0.09); the “complete relocation”of femoral heads (P= 0.61); and hypertrophy of the ligamentum
teres (P= 1.00), transverse ligaments (P = 1.00), and pulvinar (P = 1.00) were not related to RAD.
(Continued on next page)
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* Correspondence: ichbinhunger@163.com
1
Department of Radiology, Tianjin Hospital, Jiefangnan Road, Hexi District,
Tianjin 300211, TJ, China
Full list of author information is available at the end of the article
Meng et al. BMC Pediatrics (2021) 21:115
https://doi.org/10.1186/s12887-021-02587-2
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(Continued from previous page)
Conclusions: In this study, MRI can observe the variations of the abnormal soft tissue structures of the diseased
hips after CR and spica casting, and can evaluate which hips will have RAD after CR. Therefore, we can utilize MRI in
DDH patients appropriately.
Keywords: Developmental dysplasia of the hip, Closed reduction, Magnetic, Resonance imaging, Residual
acetabular dysplasia, Femoral head necrosis
Background
Developmental dysplasia of the hip (DDH) is one of the
most common musculoskeletal disorders in children, and
some patients may develop hip osteoarthritis in early
adulthood and already require joint replacement [1]. The
treatment of DDH is determined by the age at initial diag-
nosis, degree of hip dislocation, and initial therapeutic ef-
fects. Patients with DDH between 6 and 24 months or
with failed Pavlik harness treatment within 6 months are
treated with either conservative or surgical treatment mo-
dalities, such as closed reduction (CR) with spica casting
and femoral osteotomies. CR and spica casting are the
most utilized conservative treatment [2,3].
The patient needs an intraoperative X-ray arthrogra-
phy to evaluate whether CR is successful and to detect
abnormal soft tissue structures in the hip, such as hyper-
trophied acetabular cartilage, narrowed capsule, and la-
bral inversion [4,5]. A plain pelvic film was typically
used for follow-up after CR. However, X-ray films can-
not evaluate the alignment of the acetabulum and the
femoral head accurately nor observe the changes in soft
tissue structures of the hip directly [6]. Magnetic reson-
ance imaging (MRI) has no radiation and can clearly
show the soft tissue and osseous structures of the hip
joint, and its use in DDH detection and follow-up has
been increasing [7–9].
Currently, it is debated whether the abnormal soft tis-
sue structures in the hip of DDH patients can hinder CR
and affect the outcome. Renshaw et al. [10] found that
“false reduction”, where reduction was achieved immedi-
ately after CR but eventually the hip joint became un-
stable due to obstruction of soft tissue structures, can
occur in some patients. However, Druschel et al. [11] be-
lieved that abnormalities of soft tissue structures did not
affect the success of CR.
Initially, it is often impossible to obtain a concentric re-
duction in the affected hip after CR. Complete relocation
is achieved when the femoral head reaches the bottom of
the acetabulum [12]. Some authors believe that complete
relocation may increase the risk of femoral head necrosis,
which may be caused by increased pressure in the hip
joint after reduction or due to damage to the blood supply
of the femoral head when performing CR [13]. In addition,
risk factors for residual acetabular dysplasia (RAD) after
CR are also being studied extensively. Some authors
believe that the cartilaginous/osseous acetabular index,
cartilaginous/osseous central-edge angle, the shape of the
acetabular load area, and the abnormal high signal inten-
sity on T2WI of acetabular cartilage are risk factors for
RAD [14,15].
In this study, MRI was used to observe changes in the
soft tissue structure of the hip joints of DDH patients
undergoing CR. This study also aimed to explore whether
complete relocation is a risk for femoral head necrosis,
and to identify the risk factors of RAD after CR.
Methods
Tianjin Hospital Ethics Committee approved the study
(Approval number: 2017医伦审018). Informed consent
was obtained from all the parents of individual partici-
pants included in the study. The datasets used and/or
analysed during the current study are available from the
corresponding author on reasonable request.
Inclusion and exclusion criteria
In this prospective study, DDH is diagnosed if the osseous
acetabular index (OAI) > 30° [1]. The study enrolled pa-
tients aged 6–24 months with unilateral developmental
hip dislocation from October 2012 to July 2018. The ex-
clusion criteria are: 1) CR failure when performing initial
MRI, and re-dislocation at the time of replacing spica
casts; 2) poor image resolution or poor body position lead-
ing to difficulties in diagnosis; 3) hip dysplasia caused by
neuromuscular abnormalities, such as Ehlers-Danlos dis-
ease, congenital torticollis, equinovarus, arthrogryposis,
and achondroplasia. A total of 78 patients met the inclu-
sion criteria; six patients were excluded due to CR failure,
four patients due to re-dislocation, three patients due to
poor image resolution, and two patients due to other
neuromuscular abnormalities. Therefore, 63 patients (63
hips) with hip dislocation were included in this study.
Imaging examinations
Patients were examined by a plain pelvic film before and
after CR, and the degree of DDH was classified accord-
ing to the International Hip Dysplasia Institute (IHDI)
classification [16]. All patients were examined by arthro-
graphy before CR under general anesthesia. Using an 18
#
needle, 0.5–1 mL of iohexol was injected into the hip
joint space under the long adductor tendon to observe
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soft tissues in the hip. Reduction was performed using
gentle Ortolani manipulation. The hips were fixed at
flexion (90–110°) and abduction (55°) by spica casts; if
the maximal abduction angle was < 60°, adductor tenot-
omy was performed. Some patients underwent pelvic
MRI examination 1 month before CR, and all patients
underwent pelvic MRI examinations within 24 h after
CR and for follow-up before changing spica casts. Each
patient underwent MRI three to four times. All MRI ex-
aminations were performed on a 3.0 T MR scanner
(MR750, GE Healthcare, Milwaukee, WI, USA) with an
eight-channel cardiac coil. Because the patients were too
young to cooperate, diluted chloral hydrate, prepared by
dissolving 1 g of chloral hydrate in 10 mL of normal sa-
line, was injected into the anus 30 min before the MRI
examination. The injection volume of the diluted chloral
hydrate was 0.5 mL/kg. The patient laid in a supine pos-
ition, with the lower extremities naturally straightened
and the patella facing forward; the scan range was from
the iliac crest to the femoral lesser trochanter. Routine
MRI protocols and parameters of the imaging sequences
are described in Table 1. After CR and spica casting, the
patients wore a temporary night abduction brace for 3–
12 months based on the development of the diseased
hips. They also underwent pelvic X-ray examination
every half year after CR to observe the development of
the diseased hips. If a patient > 5 years old developed
RAD, we performed surgical treatment at a proper time
to resolve the RAD.
Observation and measurements
The patients changed spica casts once or twice within
4–6 months after CR and were followed up for at least
18 months.
In our study, the labro-chondral complex (LCC) was
classified into four types: type 1: normal (acetabular car-
tilage and labrum matches, the morphology of the la-
brum is triangular and outward); type 2: everted (mild
hypertrophy of acetabular cartilage, the labrum is round
and outward); type 3: partially inverted (mild or moder-
ate hypertrophy of the acetabular cartilage, the labrum
inverted partially, which inserts between the femoral
head and the acetabulum); type 4: completely inverted
(the labrum is inverted entirely and there is significant
cartilage hyperplasia) (Fig. 1).
The study observed whether the ligamentum teres, the
transverse ligament, and the pulvinar hypertrophied be-
fore and after CR. Hypertrophy of the ligamentum teres
and the transverse ligament: the ligament was thicker
than that on the normal side, and was strip-like, tortu-
ous, prolonged, and manifested mixed signal intensity;
pulvinar hypertrophy: the pulvinar was thick and visible
(Fig. 2).
The study also measured the cartilaginous acetabular
head index (CAHI) [17] of the affected hip. On the cor-
onal sequence of fat suppressed proton density weighted
imaging, the image displaying the maximal diameter of
the femoral head was selected, a vertical line was drawn
from the innermost side of the femoral head cartilage,
and the distance between the line and a line perpendicu-
lar to the outermost side of the acetabular cartilage was
measured. Another distance between the line and a line
perpendicular to the outermost side of the femoral head
cartilage was also measured. The ratio between the two
distances was the CAHI (Fig. 3).
The complete relocation rate of the femoral head at
the affected side during the last replacement of spica
casts was calculated on MRI images. On transverse and
coronal MRI images, complete relocation was accom-
plished when the inner edge of the femoral head of the
affected side completely contacts the acetabular bottom
without soft tissue structures interspersed between them
[18]. The presence of femoral head necrosis in the af-
fected hip was determined according to the Salter classi-
fication on plain radiography [19].
The OAI of the affected hip was measured on a pelvic
plain film during the last follow-up, and patients with
OAI > 25° were considered to have RAD [20]. The pa-
tients were divided into the normal acetabular group
and the RAD group.
All observations and measurements were completed
by one radiologist (MXH, with 10 years of musculoskel-
etal MRI experience). Another radiologist (WZ, with 29
years of musculoskeletal MRI experience) also classified
the LCC in the affected hips, and MXH re-classified the
complex 2 weeks after her first classification.
Statistical analysis
The study used the SPSS software (version 25.0; SPSS
Inc., Chicago, IL, USA) for statistical analysis. The
counting data were expressed as a percentage, while the
Table 1 Routine sequences and parameters of MRI examinations in the study
Sequence TR (ms) TE (ms) Bandwidth (kHz) FOV (cm) Slice thickness (mm) Slice gap (mm) Matrix NEX
Coronal FS PDWI 2500 40 85 22 × 22 3.5 0.5 320 × 224 3
Transverse FS PDWI 2500 40 63 22 × 22 3.5 0.5 320 × 256 3
Coronal T2WI 3000 85 85 24 × 16 3.5 0.5 320 × 224 6
MRI magnetic resonance imaging, TR repetition time, TE echo time, FOV field of view, NEX number of excitations, TA acquisition time, FS fat suppression, PDWI
proton density-weighted imaging
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measurement data were expressed as the mean ± stand-
ard deviation. Reliability and repeatability of LCC classi-
fication were evaluated by intraclass correlation
coefficient (ICC) and 95% confidential interval (CI). The
reliability was low when ICC < 0.5, 0.5 ~ 0.75 was
medium, 0.76 ~ 0.9 was good, and > 0.9 was excellent
[21]. After classifying the LCC, the two radiologists
made the final classification by consensus. LCC
Fig. 1 The labro-chondral complex classification. The labro-chondral complex was divided into 4 types (Coronal FS PDWI images), type 1 (a):
normal (acetabular cartilage and labrum matches, the morphology of labrum is triangular and outward); type 2 (b): everted (mild hypertrophy of
acetabular cartilage, the labrum is round and outward); type 3 (c): partially inverted (mild or moderate hypertrophy of the acetabular cartilage, the
labrum inverted partially, which inserts between the femoral head and the acetabulum); type 4 (d): completely inverted (the labrum is inverted
entirely and with significant cartilage hyperplasia)
Fig. 2 Hypertrophy of the ligamentum teres, the transverse ligament, and
the pulvinar. Hypertrophy of the ligamentum teres (red arrowhead) and
the transverse ligament (yellow arrowhead) (Coronal T2WI images): the
ligament was thicker than that in the normal side, the morphology of the
ligament was strip-like, tortuous, prolonged, and manifested mixed signal
intensity; pulvinar hypertrophy (green arrowhead): the pulvinar was thick
and visible
Fig. 3 Measurement of cartilaginous acetabular head index. Measurement
of cartilaginous acetabular head index (CAHI) of the affected hip in a DDH
patient after close reduction and spica casting: on the FS PDWI coronal
image showing the maximal diameter of the femoral head, a vertical line
was drawn from the innermost edge of the femoral head cartilage, the
distance between the line and a line perpendicular to the outermost edge
of the acetabular cartilage was measured, and another distance between
the line and a line perpendicular to the outermost edge of the femoral
head cartilage was also measured. The ratio of the two distances was the
CAHI (2.15÷2.23 × 100 = 96.4)
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classifications were analyzed before and after CR. The
trend Chi-square test or Fisher exact probability
method was used to analyze whether the hypertrophic
rates of ligamentum teres, transverse ligament, and
pulvinar in affected hips were different immediately
after CR and during follow-up. The repeated meas-
urement data analysis of variance or a Mann-Whitney
U test was used to evaluate whether the CAHI of af-
fected hips was different immediately after CR and
during follow-up. The complete relocation rate of the
affected hip at the last MRI follow-up was summa-
rized. The rate of femoral head necrosis in DDH pa-
tientswhowerefollowedupfor18monthsormore
after CR was also summarized. The Mann-Whitney U
test was used to compare the age of onset and the
follow-up time between the normal acetabular group
and RAD group. Binary logistic regression was used
to analyze whether the IHDI classification; LCC clas-
sification at the last MRI examination; hypertrophy of
ligamentum teres, transverse ligament, and pulvinar;
and complete relocation were risk factors for RAD,
using odds ratios (OR) and 95% confidence interval
(CI) to indicate the degree of risk. P< 0.05 was con-
sidered statistically significant.
Results
Patient data
A total of 63 patients (63 hips) with CR and spica cast
were included in this study, including two boys, 61 girls,
24 right hips, and 39 left hips, with an average age of
15.6 ± 4.4 months (6–23 months). Regarding the IHDI
grade, two hips were classified as grade 2, 37 were classi-
fied as grade 3, and 24 were classified as grade 4. The
average time between CR and the first spica cast change
was 70.8 ± 14 (45–100) days, and 55 patients changed
spica casts twice. The average time between the first and
second spica cast change was 67.8 ± 10.1 (45–101) days.
There were 36 patients who underwent MRI before CR,
63 patients underwent MRI immediately after CR and
the first spica casts change, and 55 patients underwent
MRI at the second time of spica casts change.
Soft tissue changes and CAHI in the affected hip before
and after CR
The inter-observer ICC of the LCC classification be-
tween the two radiologists was 0.84 (95% CI: 0.74 ~
0.91), and the intra-observer ICC was 0.94 (95% CI: 0.90
~ 0.97). The number and changes of the LCC type after
CR and at the first and second spica casts change are
listed in Fig. 4. The LCC gradually returned to its nor-
mal shape. All patients had hypertrophied ligamentum
teres, transverse ligament, and pulvinar in the affected
hips immediately before and after CR. About 70%
returned to normal for the first time of changing spica
casts, and 90% returned to normal at the second time of
changing spica casts. The detailed data are presented in
Table 2. For the patients who changed spica casts twice
(55 patients), CAHI had differences among the time
after CR, the first spica cast change, and the second
spica cast change (F = 68.0, P= 0.000). The CAHI was
68.1 ± 12.1 immediately after CR, increased to 81.2 ± 7.5
when changing casts for the first time, and 84.4 ± 7.0 in
the second spica casts change. For the patients who only
changed the casts once (eight patients), the CAHI was
60.1 ± 11.1 immediately after CR, and 81.4 ± 6.4 when
changing the casts; the CAHI was significantly increased
(Z = -3.15, P= 0.002).
The complete relocation rate and the rate of femoral
heads necrosis
MRI images showed that 58.7% (37/63) of the femoral
heads have complete relocation at the last time of chan-
ging spica casts. For patients who changed spica casts
twice, 61.8% (34/55) achieved complete relocation, while
for those who changed casts only once, 25% (2/8)
achieved complete relocation. A total of 58 patients were
followed up after CR for more than 18 months, with an
average follow-up time of 39.9 ± 12.8 (18–66) months,
and 8.6% (5/58) of the femoral heads had necrosis
(Fig. 4). The OAI was 25.0° ± 7.4° (8.2°–40.7°) in the af-
fected hips, of which 48.3% (28/58) of the OAI was no
more than 25°, indicating that the osseous acetabulum
returned to normal.
Risk factors of RAD
Of the 58 patients who were followed up after CR for
more than 18 months, eight patients changed their spica
casts only once, and the MRI follow-up time was relatively
short, so these eight patients were excluded. Among the
remaining 50 patients, 23 patients with OAI > 25° were in-
cluded in the RAD group (Fig. 5), and 27 patients with
OAI ≤25° were included in the normal acetabular group.
There was no significant difference in the age of onset be-
tween the two groups, and the follow-up time in the RAD
group was shorter than in the normal acetabular group as
shown in Table 3. Binary logistic regression analysis
showed that the morphological abnormalities of LCC at
the second time of changing spica casts were related to
RAD (OR: 4.35, 95% CI: 1.15 ~ 16.46, P= 0.03), and the
percentage of type 3 LCC was higher in the RAD group.
However, there was no significant difference in the IHDI
grade before CR (P= 0.09); complete relocation at the sec-
ond MRI examination after CR (P= 0.61); and the hyper-
trophic rates of ligamentum teres (P=1.00), transverse
ligament (P = 1.00), and pulvinar (P = 1.00) between the
two groups.
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Discussion
The study found that after 4–6 months of CR and spica
casting, the ligamentum teres, the transverse ligament,
the pulvinar, and the LCC in the affected hip joint grad-
ually returned to normal shape, and 61.8% of the femoral
head had complete relocation. The patients who
followed up for more than 18 months revealed that the
rate of the femoral head necrosis caused by CR was
about 8.6, and 48.3% of the OAI returned to normal.
Hypertrophy and partial inversion of the LCC 4–6
months after CR were risk factors for RAD, while hyper-
trophic ligaments, pulvinar, and femoral head complete
relocation had nothing to do with RAD.
In this study, LCC was classified based on MRI images.
The results show that this classification has good
consistency, high reliability, and repeatability, and can be
used in everyday work. Before CR, the labra were
everted, and during CR, the labra were caught up in the
hip joint with the reduction of the femoral head, result-
ing in labral hypertrophy and inversion. Therefore, most
of the LCC cases were type 4 and a few were type 3 im-
mediately after CR. With the gradual inward displace-
ment of the femoral head after reduction and complete
relocation, the LCC also gradually changes shape, the
labra gradually grow outward with acetabular cartilage
thinning, and it returned to the normal shape. For type
2 LCC, the everted labrum is more common in patients
with subluxation of the hip joint before CR. The labrum
is everted because of the outward and upward displace-
ment of the femoral head, which is rarely seen after CR.
There are many studies on soft tissue structures in
and around the hip joint, which hinder CR in DDH
Fig. 4 The number and changes in the labro-chondral complex (LCC) type immediately after CR and at the first and the second time of changing
spica casts
Table 2 Hypertrophic rates of the affected hips in DDH patients
Hypertrophy rate of ligamentum
teres(%)
Hypertrophy rate of transverse
ligaments(%)
Hypertrophy rate of
pulvinar(%)
Closed reduction immediately 96.4%(53/55) 94.5%(52/55) 100%(55/55)
100%(8/8) 100%(8/8) 100%(8/8)
First follow up 27.3%(15/55) 25.5%(14/55) 29.1%(16/55)
62.5%(5/8) 62.5%(5/8) 62.5%(5/8)
Second follow up 12.7%(7/55) 12.7%(7/55) 10.9%(6/55)
χ
2
value (having 3 MRI
examinations)
88.6 86.4 97.9
Pvalue (having 3 MRI
examinations)
0.000 0.000 0.000
Pvalue (having 2 MRI
examinations)
0.200 0.200 0.200
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patients [22–24]. Studer et al. [22] observed that hyper-
trophy of the ligamentum teres, transverse ligaments,
pulvinar, joint capsule, inverted labrum, and acetabular
cartilage hypertrophy were important factors that hin-
dered CR. Rosenbaum et al. [25] concluded that labral
hypertrophy and inversion, and hypertrophy of the pul-
vinar, ligamentum teres, and transverse ligaments were
the main reasons hindering CR. By arthrography and
MRI, Hattori [24] and Kim [26] found that obvious soft
tissue insertion in the hip joint, widening of the medial
contrast cistern, and LCC hypertrophy would increase
the probability of CR failure, thus increasing the need
for open surgery, even if surgical treatment cannot
achieve a good prognosis. Yuan et al. [27] found that
poor delineation of the labrum and acetabular surface
during arthrogram predicted failure of CR in children
with DDH, and medial dye pool distance ≥6 mm signifi-
cantly increased the risk of CR failure. However, the
studies by Severin [12] and Aoki [28] have shown that
the inverted labrum can be gradually shaped and
returned to a normal shape after CR without affecting
the final acetabular-head alignment. Walter et al. [29]
believed that the hypertrophy of soft tissues in the hip
joint does not lead to CR failure. The failure is due to
the mismatch between the femoral head and the acet-
abulum. Lü et al. [30] found that if the LCC was thin,
most hips could be successfully reduced and achieve
complete relocation, while patients with thick LCC
would prevent reduction of the femoral head. In our
study, the incidence of hypertrophy of the pulvinar, liga-
mentum teres, and transverse ligaments was high before
Fig. 5 A female patient 10 months after closed reduction and spica casting of the left hip joint. The patient underwent MRI examination of both
hips immediately after CR, 3 months after CR, and five and a half months after reduction. aand bshow the coronal and transverse FS PDWI
images of MRI immediately after CR. It is suggested that the LCC of the left hip is hypertrophied and completely inverted immediately after
reduction, which is considered as type 4; the ligamentum teres, transverse ligament, and pulvinar are hypertrophic. cshows that the LCC became
flattened 3 months after reduction, and the ligamentum teres, transverse ligament, and pulvinar were less hypertrophic than before. dshows that
five and a half months after reduction, the LCC still had partial inversion which was considered as a type 3 complex. The ligamentum teres,
transverse ligament, and pulvinar were not thickened and returned to normal, and the left hip joint achieved complete relocation. eshows the
pelvic X-ray film of the patient 22 months after closed reduction, the left osseous acetabular index is 33.3°, indicating that there is still residual
acetabular dysplasia; the shape of the left femoral head is intact, and no obvious abnormal density is found
Table 3 Parameters between the residual acetabular dysplasia
group and normal acetabular group
Age of onset
(month)
Follow-up time
(month)
Residual acetabular
dysplasia group
16.1 ± 4.2 36.1 ± 12.7
Normal acetabular group 14.7 ± 4.9 45.3 ± 11.8
Zvalue −0.695 −2.426
Pvalue 0.487 0.015
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and at the time of CR, but these structures gradually
returned to normal. Therefore, the authors believe that
the abnormal soft tissue structures of the affected hip
joints at reduction have no significant effect on the ul-
timate outcome, and it seems that it is not necessary to
deal with these structures at the time of reduction. The
CAHI of the affected hips increased gradually after CR,
suggesting that CR increases the stress between the fem-
oral head and the acetabulum and the cartilaginous acet-
abulum develops.
This study found that at the second time of replacing
spica casts (4–6 months after CR), most femoral heads
can achieve complete relocation, meaning that the hip
joint achieved concentric reduction. One of the most
serious complications of CR is secondary femoral head
necrosis. The cause of necrosis is unknown, but may be
related to the interruption of blood supply to the fem-
oral head, excessive abduction of the hip joint, and in-
creased stress on the femoral head. It is suggested that
the rate of femoral head necrosis after CR in patients
with DDH varies between 0 and 67% [13,31]. This study
found that the rate of femoral head necrosis with 18
months or more of follow-up after CR was 8.6%, which
was acceptable and were lower than the multicenter
study of Li et al. [3]. It was shown that with the im-
provement of orthopedic surgeons’understanding of the
“safe zone”when performing hip abduction, CR and
spica casting proved to be a safe and effective treatment
for 6–24-month-old DDH patients.
In this study, it was found that partial inversion of
the labrum at 4–6 months after CR was a risk factor for
RAD, while complete relocation of the femoral head
does not influence the development of osseous acetabu-
lum. Some risk factors of RAD have been found [32];
however, these factors are still controversial, and there
is a lack of in-depth research on the causes of abnormal
signals and parameters of acetabular cartilage. We have
conducted a study on the application of T2 mapping
combined with CUBE [33], which found that the T2
values of acetabular and femoral head cartilage in pa-
tients with inverted labra were higher than those in pa-
tients without labra inversion, and the more serious the
labral inversion, the higher the T2 value, suggesting
that the acetabular cartilage in patients with labral in-
version was mostly made of hyaline cartilage with in-
creased free water content, and it could not be
mineralized in time. Combined with this study, we be-
lieve that labral inversion can hinder the normal ossifi-
cation of the acetabular cartilage, resulting in RAD
after reduction. The complete relocation of the femoral
head suggests that CR can achieve a concentric reduc-
tion of the hip in patients with DDH, but if the labral
inversion persists, it will hinder the normal develop-
ment of acetabular cartilage.
This study has some limitations. First, the sample size
in the RAD group and the normal acetabular group in-
cluded in this study was small, and the diagnostic effi-
ciency was insufficient. It is necessary to further increase
the number of patients in each group in the future. Sec-
ond, the follow-up time of the patients after CR was un-
even and relatively short, without follow-up until the
patients grew up, and the outcome of the condition of
the patients was unknown. The follow-up time of the
normal acetabular group is longer than that of the RAD
group, so there may be some patients in the RAD whose
OAI returned to normal with time. Therefore, it is ne-
cessary to continue long-term follow-up in these pa-
tients to observe the outcome. Lastly, the use of MRI
repeatedly in young children is impractical in the clinical
setting because of compliance, need for anesthesia, and
expenses; therefore, it is very difficult to perform MRI
examinations universally.
Conclusion
In this study, MRI can observe the variations of the ab-
normal soft tissue structures of the diseased hips after
CR and spica casting, and can evaluate which hips will
have RAD after CR. Therefore, we can utilize MRI in
DDH patients appropriately.
Abbreviations
DDH: Developmental dysplasia of the hip; CR: Closed reduction;
MRI: Magnetic resonance imaging; RAD: Residual acetabular dysplasia;
OAI: Osseous acetabular index; IHDI: International Hip Dysplasia Institute;
LCC: Labro-chondral complex; CAHI: Cartilaginous acetabular head index;
ICC: Intraclass correlation coefficient; CI: Confidential interval
Acknowledgements
The authors thank Zhongli Zhang and Huadong Zhang of the Department
of Orthopedic Pediatrics, Tianjin Hospital, Tianjin, Jiefangnan Road, Hexi
District, Tianjin, TJ 300211, China. The authors also thank Editage (www.
editage. cn) for English language editing.
Authors’contributions
XHM and ZW collected the data and wrote the draft. JPY contributed to the
elaboration of the ideas developed in the manuscript and made critical
amendments. The authors have read and approved the final manuscript.
Funding
Not Applicable.
Availability of data and materials
Most of the data supporting our findings are contained within the
manuscript, and all others will be shared upon request.
Declarations
Ethics approval and consent to participate
Tianjin Hospital Ethics Committee had approved the study (Approval
number: 2017医伦审018). Informed consent was obtained from all the
parents of individual participants included in the study. All methods were
performed in accordance with the Declaration of Helsinki.
Consent for publication
Not Applicable.
Meng et al. BMC Pediatrics (2021) 21:115 Page 8 of 9
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Department of Radiology, Tianjin Hospital, Jiefangnan Road, Hexi District,
Tianjin 300211, TJ, China.
2
Department of Orthopedic Pediatrics, Tianjin
Hospital, Jiefangnan Road, Hexi District, Tianjin 300211, TJ, China.
Received: 23 December 2020 Accepted: 1 March 2021
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